The disclosure relates to a hydraulic circuit device suitable for being applied to a valve body in a power train, especially a hybrid drive system, mounted in a vehicle. More particularly, the disclosure relates to a drain of a hydraulic circuit device.
A power train, such as an automatic transmission or a hybrid drive system, mounted in a vehicle typically includes a hydraulic circuit device which supplies oil that serves as lubrication oil or working oil. The hydraulic circuit device includes a valve body and various valves arranged within the valve body. The valve body is arranged in an oil pan provided in a lower portion of a case of the automatic transmission or hybrid drive system.
An oil strainer is arranged underneath the valve body. Oil in the oil pan is drawn up through the oil strainer, and the pressure of the oil is then regulated and switched appropriately by a changeover valve such as a shift valve, a pressure regulating valve such as a regulator valve or a modulator valve, and another valve such as a check valve. After being regulated and switched, the oil is then supplied, either as working oil, to the various hydraulic servos of the automatic transmission or hybrid drive system, or as lubrication oil, to the areas that need lubricating.
Formed in the valve body are a cylindrical valve hole which houses various valves, a communicating passage that is connected to a port of each valve, and a drain hole which provides communication between the valve hole and an external portion. Based on the switching position of the changeover valve, communication is opened between an input port and a drain port such that excess oil at the pressure regulating valve is released through the drain port. The oil from the drain port is then discharged outside the valve body where it is recovered to the oil pan (see Japanese Patent Application Publication No. JP-A-10-184859).
In the related art, the drain hole opens at a central portion of a valve hole in a valve body such that drain oil from the drain port of each valve is quickly discharged from the drain hole to the outside.
The related art has the drain hole formed near the apex of a cylindrical bulging portion of a valve body in which the valve hole is formed (see reference character 25e in FIG. 3). This structure has an excellent oil discharge capability because oil discharged from the drain port of the valve flows directly into the oil pan from the drain hole corresponding to the drain port. However, solid debris (foreign matter), such as metal dust and bits of resin mixed in with the oil in the oil pan, can easily enter the valve hole from the drain hole. When foreign matter enters the valve port and spool, it may cause the valve to stick.
In particular, a hybrid drive system is provided with electric motors (a control motor and a drive motor) so lubrication oil flows to cool the motors. At that time, insulating material, such as varnish used to coat the coils, peels off and mixes in the form of resin (coating) bits with the oil. In particular, in the case of vehicles provided with an FR hybrid drive system, a drive motor with increasingly large capacity is used for larger vehicles. Large capacity drive motors generate a large amount of heat, which means that a large amount of oil is used to cool the drive motor. This, combined with the fact that the oil pan is arranged at the lower portion of the drive motor case, results in a tendency for oil containing large amounts of resin bits to be circulated directly back to the oil pan.
Due to their respective specific gravities, the metal dust sinks to the bottom of the oil pan while the bits of resin are suspended in the oil. Therefore, while not much metal dust enters the valve hole through the drain hole in the valve body that is positioned in the upper portion of the oil pan, it is highly likely that bits of resin will enter the valve hole through the drain hole.